1. Field of the Invention
The present invention generally relates to an apparatus and method for adsorbing fuel vapor and thereafter desorbing and supplying a sufficient amount of the vaporized fuel necessary to start an internal combustion engine using only the fuel vapor.
2. Description of the Related Art
Although catalytic converters are well known for reducing oxides of nitrogen (NOx), and oxidizing hydrocarbons and carbon monoxide from automobile exhaust, these reactions typically take place after the catalyst has attained its light-off temperature, at which point the catalyst begins to convert the hydrocarbons to harmless gases. The typical catalytic light-off time for most internal combustion engine systems is around 50 to 120 seconds (generally in the temperature range of 200-350.degree. C.), although the actual catalytic light-off time for any system depends on various factors; including, for instance, the aging of the catalyst. Seventy to almost ninety five percent of hydrocarbon emissions from automotive vehicles are emitted during this first minute, or so, of "cold start" engine operation. As the standards relating to emission control of automobiles become more stringent, increasing the effectiveness of automotive emission control systems by reducing the amount of hydrocarbons discharged into the atmosphere during cold-start has become increasingly important.
Cold-start engine systems utilizing fuel vapor-purging methods for internal engines are widely known and have been investigated as system solutions for reducing cold-start emissions. Generally, these systems include a canister having activated charcoal or other hydrocarbon adsorbing material for adsorbing fuel vapor generated from the fuel tank in the form of packed pellet bed, a purging passage connecting between the canister and the intake passage for purging a mixture of the fuel vapor and air therethrough into the intake passage. When starting the engine in a cold-start condition these systems generally operate to supply the engine with both fuel injected from the fuel injection valves as well as fuel vapor purged from the canister. Representative systems include, Japanese Provisional Utility Model Publication (Kokai) No. 3-97560, U.S. Pat. Nos. 5,224,456 (Hosoda et al) 5,349,934 (Miyano), and 5,482,023 (Hunt et al.). While these systems have improved exhaust emission characteristics, they still involve injecting a portion of liquid fuel into the intake chamber without the fuel being vaporized, which during cold-start conditions results in some part of this liquid fuel attaching to the intake walls and thereafter being emitted as unburnt hydrocarbons.
An improvement over the above standard cold-start systems is disclosed in U.S. Pat No. 5,474,047 (Cochard et al.) wherein it describes a process for supplying fuel to an internal combustion engine with controlled fuel injection and comprising a controlled fuel vapor recovery system. During cold-start operating phases of the engine, the fuel injectors remain inoperative for a given period while the fuel vapors trapped in the recovery system are recycled into the intake circuit of the engine. Although this reference discloses a "vapor-only" process cold-start engine system, this system suffers from a number of disadvantages. (1) electrically heating the adsorber filter from the outside is likely to result in slower than industry desired vapor desorption, i.e., a system in which starting of the engine is delayed; (2) absence of a mechanism in the system to guarantee that there is sufficient vapor available to start the engine; and, (3) this system having a activated carbon packed bed pellet configuration is likely to generate insufficient vapor as a result the inherent high pressure drop associated with packed bed configurations.
Notwithstanding the foregoing developments, work has continued to discover and provide new engine systems not only capable of meeting the stricter governmental emission standards but which are also capable of consistently and quickly "vapor-only" starting.